The information below is from UKmap Edition 23 (Oct 2019 version)
The total areas of buildings in retail distribution places in London is 2,375.76 ha.
The total areas of hard standing1 in retail distribution places London is 1,779.18 ha. This figure covers retail car parking space but also other man-made surfaces. The exact area of car parking space alone cannot be extracted from the data held by the GLA.
1 Hard standing: All areas that are not part of the transport network but which form areas of man-made surface, usually impervious, such as tarmac or concrete. These will include small areas of pavement leading to non-residential buildings, private car parking, public car parks and various man-made surfaces such as loading areas etc.
The car park areas provided below only include non-retail car parking space across London.
Total areas of multi storey car parking = 32.17ha
Total areas of street level car park =264.79 ha